In the LM317 datasheet it says that the thermal resistance from the junction-to-case (top) thermal resistance is ~16C/W. That seems al little high does that mean to the metal tab or what does that mean because the junction-to-board thermal resistance (~5C/W) seems a little closer to what I would expect. Also, what is the formula for adding together various (heat sink, junction to tab, etc.) thermal resistances to ultimately get the max power dissipation by applying to the maximum temperature rating?
